Delegated properties

Kotlin enhances the concept of properties to promote code reuse and make the developer coding task easier. There are many repetitive code snippets you and I could write. Ideally, we should have the following functionality out-of-the-box:

1. A property value should be computed lazily on its first ever access.

2. Notify the listeners of a change to one of the values of properties. Have you ever coded in C#? If yes, I am sure the INotifyPropertyChange interface will come to mind.

3. Use a map to store your fields rather than a materialized field.

Well, good news! Kotlin's delegate properties support all of these. We deal quite often with types for which we need an identifier:

    interface WithId { 
      val id: String 
    } 
 
    data class WithIdImpl(override val id: String) : WithId 
 
    class Record(id: String) : WithId by Record.identifier(id) { 
      companion object Record { 
        fun identifier(identifier: String) = WithIdImpl...